Twire
This plugin will extend Buddypress to have Twitter and BuddyPress combined to get a Twire.

Twitme
This plugin allows you to automatically post your new posts on the twitter website.

Twitter Blaster
Twitter Blaster is a plugin that will allow your visitors to post to your Twitter account. Once installed it, your users can update your Twitter. Twitter Blaster will post the users submission as a pending post. Thrn you can approve them as a twitter update and/or a post. You can also delete any spam post.

Twitter Digest
This plugin uses the pseudo-cron facility available in WordPress to publish a daily post of tweets from the previous day. It is based on Alex King’s Twitter Tools.

Twitter Feed
The control functions such as connecting to a Twitter account and storing information on the tweets/blogs, can be accessed through the “Twitter Control” in the WordPress admin panel. Any changes in the currently active Twitter account tweets can be immediately updated by clicking on the “Update Blogs” button.

Twitter It
With this plugin an user has the ability to twitter a article that he is your site. So just place the “Twitter it!” template-tag next to your article and every user who reads your article and wants to twitter it all over the web just has to click the “Twitter it!” link.

Twitter Links
This plugin will convert valid Twitter usernames mentioned in comments into a link to their Twitter profile page.

Twitter News Feed
The plugin has a specific use case, that is to import tweets from defined Twitter users containing specific hashtags into WordPress.

Twitter Poster
The Twitter Poster allows wordpress publishers to automatically post their new posts to their Twitter account. It will take the title of a new post and will submit it to the Twitter account specified in the options. It will also add the link back to the post, allowing your twitter followers to access the post details.

Twitter ReTweet
By using the plugin you could use to output a basic, stylable link anywhere on a WordPress post or page which, when clicked, would allow visitors to quickly and easily ReTweet the current post.

Twitter style links
If you write something like “@grayme, how are you?” this plugin will search for @grayme’s url in the comment list of the current post and will convert his/her name to a link.

Twitter Tag
It adds a Twitter @username in your blog post and automatically create a link to that users Twitter page and send a tweet telling them that they’ve been tagged in one of your posts. It uses Tiny URL to include a URL to the blog post in the tweet.

Twitter Tools
Alex King and his infamous set of wordpress/twitter tools

Twitter Updater
This plugin will let you automatically update your Twitter.com status with your most recent blog post. There are a few options to how the display will look when it updates.

Twitter User
Twitter User is a simple plugin which adds an additional field to the authors profile in which they can add their twitter username.

Wickett Twitter Widget
Display tweets from a Twitter account in the sidebar of your blog. As seen on WordPress.com.

WordPress Twitter Widget
Using the Javascript, adds a sidebar widget to display Twitter updates. It’s not sophisticated and there’s only 3 configuration options: Twitter account name, widget title and number of updates you want shown.

WordTwit
WordTwit is a plugin that utilizes the Twitter API to automatically push a published post to your Twitter account as a tweet.

WP to Twitter
Posts a Twitter status update when you update your WordPress blog or post to your blogroll, using the Cligs URL shortening service.

WP Twitter Pitch
WP-TwitterPitch is all about getting the pitch delivered to you in the form you want to get it delivered – in other words in Twitter format.